What is the code in Java?

Problem A: Combination Input Standard Input A Output Standard Output Time Limit 2 seconds Problem Description You have the first N capital of the alphabet. You need to output all possible combinations of K length. Order the combinations alphabetically. Input The first line of the input gives an integer T, which is the number of test cases. Each test case consists of two integers N and K. Output Each case consists of a single line with the format "Case #i:", where i represents the case number and followed by output all possible K size combinations of the first N capital letters. Each combination should be in a single line. Output a new line after each test case